The present invention relates to a milling machine with a mill head having a cutting stroke across the face of the workpiece and a return stroke retracted from the face of the workpiece to prevent cutting on return.
In milling surfaces on a workpiece it is common practice to move the mill head across the workpiece surface to be finished and then to return the mill head to its original position in preparation for cutting the next workpiece. The feed rate of the mill head in the cutting stroke is quite slow in comparison to the rate of return of the mill head. In doing so it is common for the mill head cutters to leave an undesirable trace cut on the workpiece surface on the return stroke. This is especially true where the return stroke is rapid. The undesirable trace can be minimized if a slower return stroke is used. This, however, results in an overall reduction in production rate and efficiency of the milling station. On the other hand a separate slide could be used to retract the entire milling head assembly on the return stroke. This, however, results in a complex, expensive construction.
In the present invention, a milling machine is provided with the milling head assembly including a piston structure which is hydraulically actuated to advance the mill head cutters to their cutting position and resiliently, spring biased to move the mill head cutters to a retracted, non-cutting position. Thus in the cutting stroke the piston structure is hydraulically actuated to move and hold the mill head cutters in their advanced cutting position overcoming the spring bias urging them to a retracted position. After the cutting stroke is completed the fluid pressure is relieved and the spring bias moves the piston structure and mill head cutters slightly to their retracted position assuring that the mill head cutters will not engage the workpiece face on the return stroke; while in this retracted position the milling head assembly is quickly returned past the workpiece with the mill head cutters in clearance relationship with the previously milled workpiece surface. Thus the return stroke can be rapid, i.e. 10 to 15 times faster than the cutting stroke, and the piston structure can be again hydraulically actuated to move the mill head cutters to their advanced, cutting position in preparation for the cutting stroke on the next workpiece. Thus in the present invention substantially only the mill head cutters are reciprocated between the cutting position for the cutting stroke and the retracted position for the return stroke; this results in a more simple and less expensive structure in comparison to one in which the entire milling head assembly would be reciprocated between cutting and retracted positions.
The apparatus can also be operated to finish a workpiece surface in a unique manner. In this regard, the workpiece is located such that when in the retracted position the mill head cutters will make a first rough cut across the surface. On the next cutting stroke, the mill head cutters will be moved to the advanced position for the finish cut and then retracted for the return stroke.
Thus it is an object of the present invention to provide a new and improved milling machine with a retractible mill head structure.
It is another object to provide a new and unique procedure for rough and finish cutting of a workpiece surface.
It is a general object to provide a new and improved milling machine.